PROJECT SUMMARY/ABSTRACT Sports-related concussion is a major public health concern. Many children participate in organized sports, thus exposing them to potential brain injury at earlier ages. While impacts to the head in contact sports (CS) are unavoidable and can cause serious consequence such as concussion, non-concussive repetitive head impacts (RHI) happen much more often and are implicated as a source for the deterioration of cerebral structure and function later in life. Emerging evidence suggests that effects of repetitive blows to the head are cumulative and that RHI exposure during CS is connected to pathologically altered neurophysiology. Despite its high incidence, the pathophysiology of brain injury due to repetitive subconcussive impacts remains elusive. The overarching goal of this research is to combine state-of-art neuroimaging and biomechanical metrics to identify key neurophysiological processes in young athletes associated with RHI exposure during routine CS. We will conduct a longitudinal study to systematically characterize neuroimaging biomarkers of underlying neurophysiological changes induced by RHI exposure during routine CS in young athletes. We will investigate two age groups (middle school and high school) of CS players in comparison with closely matched non-contact sports (NCS) players at two consecutive game and practice seasons. Each subject will be assessed four times: right before and after each season. The biomechanical doe of RHI will be assessed using the impact monitoring mouthguard system for CS players. This study is aimed to determine effects of RHI exposure on changes in brain structure and function, the relationship between biomechanical dose of RHI and its effects on brain structure and function in CS athletes, as well as age effects on non-concussive brain injury after exposure to RHI during routine CS season. Findings from the proposed research will have important clinical significance, with the potential to enhance the capacity to detect sports-related non-concussive injury due to RHI exposure, monitor its recovery, and serve as a potential biomarker for response to treatment interventions in the future.